Asymmetric hydrogenation of olefins, a Nobel Prize winning reaction, is now ubiquitous in both research and industrial laboratories. Present technologies rely upon precious metal catalysts (Rh, Ir, Ru, Pd, Pt, etc.) in conjunction with chiral phosphine ligands to accomplish the asymmetric hydrogenation of olefins. These metals and ligands are expensive when compared to base metals such as iron. Thus, there is an incredible cost incentive to use base-metal catalysts, which can be orders of magnitude less expensive than their precious metal counterparts. The precious metals and the phosphine ligands are also toxic. Additional measures must therefore be taken to remove the catalyst system from the hydrogenated products following hydrogenation.
Aryl-substituted bis(imino)pyridine iron and cobalt compounds have emerged as an effective class of base metal olefin hydrogenation catalysts. Each of Bouwkamp, M. W. et al. (J. Am. Chem. Soc. 2005, 127, 9660-9661), Bouwkamp, M. W. et al. (Chem. Commun. 2005, 3406-3408), Fernández, I. et al. (Organometallics 2008, 27, 109-118), and Trovitch, R. J. et al. (J. Am. Chem. Soc. 2008, 130, 11631-11640) discloses four or five coordinate iron compounds that have κ3-bis(imino)pyridyl ligands bound thereto. In each case, the κ3-bis(imino)pyridyl ligands were achiral or symmetric and achiral. Some of these iron compounds were shown to catalyze olefin polymerizations, but there is no disclosure in any of these references of hydrogenating or transforming olefins (preferably prochiral) and alkynes. There is also no disclosure that these compounds would be useful for such reactions.
Cobalt compounds having κ3-bis(imino)pyridyl ligands are also known in the art. Each of Knijnenburg, Q. et al. (J. Mol. Catal. A 2005, 232, 151-159), Humphries, M. J. et al. (Organometallics 2005, 24, 2039-2050), Gibson, V. C. et al. (Chem. Commun. 2002, 2316-2317), Tellmann, K. P. et al. (Organometallics 2004, 23, 5503-5513), and Zhu et al. (Organometallics 2010, 29, 1897-1908) discloses four or five coordinate cobalt compounds that have κ3-bis(imino)pyridyl ligands bound thereto. The κ3-bis(imino)pyridyl ligands in these disclosures are symmetric and achiral, and the compounds having these ligands were shown to be useful for polymerization and hydrogenation of α-olefins. However, these references also fail to disclose hydrogenating or transforming further substituted olefins (preferably prochiral) and alkynes or that such compounds would be useful for these reactions. Accordingly, modified ligand architectures are required to generate single enantiomer catalysts for asymmetric olefin hydrogenation and for transformation of olefins and alkynes.
Bianchini et al. (Eur. J. Inorg. Chem. 2003, 1620-1631) discloses a modified ligand architecture, which is a C1 symmetric κ3-bis(imino)pyridyl ligand where the nitrogen atom of one imine moiety has a large 2,6-diisopropyl aryl ring bonded thereto and the nitrogen atom of the other imine moiety has a chiral group. These ligands were bound to cobalt and iron dihalide sources to form five coordinate dihalide compounds, which were shown to be useful, when combined with methylaluminoxane (MAO), for ethylene polymerization. Bianchini and coworkers have also disclosed transition metal compounds having κ3-thiophenyl(imino)pyridyl ligands, and the use of these compounds for the polymerization/oligomerization of ethylene/α-olefins in U.S. Pat. Nos. 6,927,313 and 6,916,931. However, there is no disclosure in these references of hydrogenating prochiral olefins in the presence of these transition metal compounds, nor is there any disclosure that the compounds disclosed therein would be efficient for this reaction.
In view of the foregoing, there is a need for compounds comprised of first row transition metals and ligands operable for the hydrogenation of olefins, preferably prochiral olefins, and/or the transformation of alkynes. The present inventors have provided a solution to this problem with the invention disclosed herein.